Which planet spins the fastest? | Cool Cosmos Which planet spins the fastest? Jupiter is the fastest spinning planet in our Solar System rotating on average once in just under 10 hours. That is very fast especially considering how large Jupiter is. This means that Jupiter has the shortest days of all the planets in the Solar System. Since Jupiter is a gas planet, it does not rotate as a solid sphere. Jupiter's equator rotates a bit faster than its polar regions at a speed of 28,273 miles/hour (about 43,000 kilometers/hour). Jupiter's day varies from 9 hours and 56 minutes around the poles to 9 hours and 50 minutes close to the equator. Continue the conversation on Solar System Planets: Order of the 8 (or 9) Planets Solar System Planets: Order of the 8 (or 9) Planets By Robert Roy Britt | January 22, 2016 12:35pm ET MORE The planets of the solar system as depicted by a NASA computer illustration. Orbits and sizes are not shown to scale.

Credit: NASA Ever since the discovery of Pluto in 1930, kids grew up learning about the nine planets of our solar system. That all changed starting in the late 1990s, when astronomers began to argue about whether Pluto was a planet. In a highly controversial decision , the International Astronomical Union ultimately decided in 2006 to call Pluto a “dwarf planet,” reducing the list of “real planets” in our solar system to eight. However, astronomers are now hunting for another planet in our solar system, a true ninth planet , after evidence of its existence was unveiled on Jan. 20, 2016. The so-called "Planet Nine," as scientists are calling it, is about 10 times the mass of Earth and 5,000 times the mass of Pluto. [ Solar System Pictures: A Photo Tour ] If you insist on including Pluto , then that world would come after Neptune on the list; Pluto is truly way out there, and on a wildly tilted, elliptical orbit (two of the several reasons it got demoted). Interestingly, Pluto used to be the eighth planet, actually. More on that below.

Terrestrial planets The inner four worlds are called “ terrestrial planets ,” because, like Earth, their surfaces are all rocky. Pluto, too, has a solid surface (and a very frozen one) but has never been grouped with the four terrestrials. Jovian planets The four large outer worlds — Jupiter, Saturn, Uranus, and Neptune — are known as the “Jovian planets” (meaning “Jupiter-like”) because they are all huge compared to the terrestrial planets, and because they are gaseous in nature rather than having rocky surfaces (though some or all of them may have solid cores, astronomers say). According to NASA , "two of the outer planets beyond the orbit of Mars — Jupiter and Saturn — are known as gas giants; the more distant Uranus and Neptune are called ice giants." This is because, while the first two are dominated by gas, while the last two have more ice. All four contain mostly hydrogen and helium.

Dwarf planets The IAU definition of a full-fledged planet goes like this: A body that circles the sun without being some other object's satellite, is large enough to be rounded by its own gravity (but not so big that it begins to undergo nuclear fusion, like a star) and has "cleared its neighborhood" of most other orbiting bodies. Yeah, that’s a mouthful. The problem for Pluto, besides its small size and offbeat orbit, is that it shares its space with lots of other objects in the Kuiper Belt , beyond Neptune. Still, the demotion of Pluto remains controversial . The IAU planet definition puts other small, round worlds in the dwarf planet category, including the Kuiper Belt objects Eris , Haumea , and Makemake . Also now a dwarf planet is Ceres , a round object in the Asteroid Belt between Mars and Jupiter. Ceres was actually considered a planet when discovered in 1801 and then later deemed to be an asteroid.

Some astronomers like to consider Ceres as a 10th planet (not to be confused with Nibiru or Planet X ), but that line of thinking opens up the possibility of there being 13 planets, with more bound to be discovered. The planets Below is a brief overview of the eight primary planets in our solar system , in order from the inner solar system outward: Mercury The closest planet to the sun, Mercury is only a bit larger than Earth's moon. Its day side is scorched by the sun and can reach 840 degrees Fahrenheit (450 Celsius), but on the night side, temperatures drop to hundreds of degrees below freezing. Mercury has virtually no atmosphere to absorb meteor impacts, so its surface is pockmarked with craters, just like the moon. Over its four-year mission, NASA's MESSENGER spacecraft has revealed views of the planet that have challenged astronomers' expectations. Discovery: Known to the ancients and visible to the naked eye Named for: Messenger of the Roman gods Diameter: 3,031 miles (4,878 km) Orbit: 88 Earth days Venus' southern hemisphere, as seen in the ultraviolet.

Credit: ESA Venus The second planet from the sun, Venus is terribly hot, even hotter than Mercury. The atmosphere is toxic. The pressure at the surface would crush and kill you. Scientists describe Venus’ situation as a runaway greenhouse effect. Its size and structure are similar to Earth, Venus' thick, toxic atmosphere traps heat in a runaway "greenhouse effect." Oddly, Venus spins slowly in the opposite direction of most planets. The Greeks believed Venus was two different objects — one in the morning sky and another in the evening. Because it is often brighter than any other object in the sky — except for the sun and moon — Venus has generated many UFO reports. Discovery: Known to the ancients and visible to the naked eye Named for: Roman goddess of love and beauty Diameter: 7,521 miles (12,104 km) Orbit: 225 Earth days An image of the Earth taken by the Russian weather satellite Elektro-L No.1. Credit: NTsOMZ Earth The third planet from the sun, Earth is a waterworld, with two-thirds of the planet covered by ocean. It’s the only world known to harbor life. Earth’s atmosphere is rich in life-sustaining nitrogen and oxygen.

Earth's surface rotates about its axis at 1,532 feet per second (467 meters per second) — slightly more than 1,000 mph (1,600 kph) — at the equator. The planet zips around the sun at more than 18 miles per second (29 km per second). Diameter: 7,926 miles (12,760 km) Orbit: 365.24 days Day: 23 hours, 56 minutes Related: Mars researchers are focusing both Earth-based and planet orbiting sensors to better understand sources of methane on the red planet. Image Credit: Space Telescope Science Institute Mars The fourth planet from the sun, is a cold, dusty place. The dust, an iron oxide, gives the planet its reddish cast. Mars shares similarities with Earth: It is rocky, has mountains and valleys, and storm systems ranging from localized tornado-like dust devils to planet-engulfing dust storms. It snows on Mars. And Mars harbors water ice. Scientists think it was once wet and warm, though today it’s cold and desert-like.

Mars' atmosphere is too thin for liquid water to exist on the surface for any length of time. Scientists think ancient Mars would have had the conditions to support life, and there is hope that signs of past life — possibly even present biology — may exist on the Red Planet. Discovery: Known to the ancients and visible to the naked eye Named for: Roman god of war Diameter: 4,217 miles (6,787 km) Orbit: 687 Earth days Day: Just more than one Earth day (24 hours, 37 minutes) Related: Close-up of Jupiter's Great Red Spot as seen by a Voyager spacecraft. Credit: NASA/JPL-Caltech Jupiter The fifth planet from the sun, Jupiter is huge and is the most massive planet in our solar system. It’s a mostly gaseous world, mostly hydrogen and helium. Its swirling clouds are colorful due to different types of trace gases. A big feature is the Great Red Spot, a giant storm which has raged for hundreds of years. Jupiter has a strong magnetic field, and with dozens of moons, it looks a bit like a miniature solar system.

Discovery: Known to the ancients and visible to the naked eye Named for: Ruler of the Roman gods Diameter: 86,881 miles (139,822 km) Orbit: 11.9 Earth years The shadow of Saturn's moon Mimas dips onto the planet's rings and straddles the Cassini Division in this natural color image taken as Saturn approaches its August 2009 equinox. Credit: NASA/JPL/Space Science Institute Saturn The sixth planet from the sun is known most for its rings . When Galileo Galilei first studied Saturn in the early 1600s, he thought it was an object with three parts. Not knowing he was seeing a planet with rings, the stumped astronomer entered a small drawing — a symbol with one large circle and two smaller ones — in his notebook, as a noun in a sentence describing his discovery. More than 40 years later, Christiaan Huygens proposed that they were rings. The rings are made of ice and rock. Scientists are not yet sure how they formed. The gaseous planet is mostly hydrogen and helium. It has numerous moons .

Discovery: Known to the ancients and visible to the naked eye Named for: Roman god of agriculture Diameter: 74,900 miles (120,500 km) Orbit: 29.5 Earth years Day: About 10.5 Earth hours Related: Near-infrared views of Uranus reveal its otherwise faint ring system, highlighting the extent to which the planet is tilted. Credit: Lawrence Sromovsky, (Univ. Wisconsin-Madison), Keck Observatory Uranus The seventh planet from the sun, Uranus is an oddball. It’s the only giant planet whose equator is nearly at right angles to its orbit — it basically orbits on its side. Astronomers think the planet collided with some other planet-size object long ago, causing the tilt. The tilt causes extreme seasons that last 20-plus years, and the sun beats down on one pole or the other for 84 Earth-years. Uranus is about the same size as Neptune. Methane in the atmosphere gives Uranus its blue-green tint. It has numerous moons and faint rings.

Discovery: 1781 by William Herschel (was thought previously to be a star) Named for: Personification of heaven in ancient myth Diameter: 31,763 miles (51,120 km) Orbit: 84 Earth years Neptune’s winds travel at more than 1,500 mph, and are the fastest planetary winds in the solar system. Credit: NASA/JPL Neptune The eighth planet from the sun, Neptune is known for strong winds — sometimes faster than the speed of sound. Neptune is far out and cold. The planet is more than 30 times as far from the sun as Earth. It has a rocky core. Neptune was the first planet to be predicted to exist by using math, before it was detected. Irregularities in the orbit of Uranus led French astronomer Alexis Bouvard to suggest some other might be exerting a gravitational tug. German astronomer Johann Galle used calculations to help find Neptune in a telescope. Neptune is about 17 times as massive as Earth. Discovery: 1846 Pluto and its moons orbit the sun near the edge of our solar system.

Learn all about Pluto's weirdly eccentric orbit, four moons and more in this Space.com infographic . Credit: SPACE.com/Karl Tate Pluto (Dwarf Planet) Once the ninth planet from the sun, Pluto is unlike other planets in many respects. It is smaller than Earth's moon. Its orbit carries it inside the orbit of Neptune and then way out beyond that orbit. From 1979 until early 1999, Pluto had actually been the eighth planet from the sun. Then, on Feb. 11, 1999, it crossed Neptune's path and once again became the solar system's most distant planet — until it was demoted to dwarf planet status. Pluto will stay beyond Neptune for 228 years. Pluto’s orbit is tilted to the main plane of the solar system — where the other planets orbit — by 17.1 degrees. It’s a cold, rocky world with only a very ephemeral atmosphere. NASA's New Horizons mission performed history's first flyby of the Pluto system on July 14, 2015.

[Related: New Horizons' Pluto Flyby: Latest News, Images and Video ] Discovery: 1930 by Clyde Tombaugh Named for: Roman god of the underworld, Hades Diameter: 1,430 miles (2,301 km) Orbit: 248 Earth years NASA Solar System Exploration: Dwarf Planets Planet Nine Planet Nine orbits the sun at a distance that is 20 times farther out than the orbit of Neptune. (The orbit of Neptune is 2.7 billion miles from the sun at its closest point.) The strange world's orbit is about 600 times farther from the sun than the Earth's orbit is from the star. Scientists have not actually seen Planet Nine directly . Its existence was inferred by its gravitational effects on other objects in the Kuiper Belt, a region at the fringe of the solar system that is home to icy objects left over from the birth of the sun and planets. Planet Mercury: Facts About the Planet Closest to the Sun Planet Mercury: Facts About the Planet Closest to the Sun By Charles Q.

Choi, Space.com Contributor | November 30, 2016 08:44pm ET MORE This view is one of the first from the MESSENGER probe's Oct. 6, 2008 flyby of Mercury. Credit: NASA/JHUAPL/CIW Mercury is the closest planet to the sun. As such, it circles the sun faster than all the other planets, which is why Romans named it after their swift-footed messenger god. The Sumerians also knew of Mercury since at least 5,000 years ago. It was often associated with Nabu, the god of writing . Mercury was also given separate names for its appearance as both a morning star and as an evening star. Greek astronomers knew, however, that the two names referred to the same body. Heraclitus believed that both Mercury and Venus orbited the sun, not Earth. [ Latest Photos: Mercury Seen by NASA's Messenger Probe ] Mercury's physical characteristics Because the planet is so close to the sun, Mercury's surface temperature can reach a scorching 840 degrees Fahrenheit (450 degrees Celsius).

However, since this world doesn't have a real atmosphere to entrap any heat, at night temperatures can plummet to minus 275 F (minus 170 C), a temperature swing of more than 1,100 degrees F (600 degree C), the greatest in the solar system. Mercury is the smallest planet — it is only slightly larger than Earth's moon. Since it has no significant atmosphere to stop impacts, the planet is pockmarked with craters. About 4 billion years ago, an asteroid roughly 60 miles (100 kilometers) wide struck Mercury with an impact equal to 1 trillion 1-megaton bombs, creating a vast impact crater roughly 960 miles (1,550 km) wide. Known as the Caloris Basin, this crater could hold the entire state of Texas. Another large impact may have helped create the planet's odd spin . As close to the sun as Mercury is, in 2012, NASA's MESSENGER spacecraft discovered water ice in the craters around its north pole, where regions may be permanently shaded from the heat of the sun.

The southern pole may also contain icy pockets, but MESSENGER's orbit did not allowed scientists to probe the area. Comets or meteorites may have delivered ice there, or water vapor may have outgassed from the planet's interior and frozen out at the poles. [Related: First Photos of Water Ice on Mercury Captured by NASA Spacecraft ] As if Mercury isn't small enough, it not only shrank in its past but is continuing to shrink today . The tiny planet is made up of a single continental plate over a cooling iron core. As the core cools, it solidifies, reducing the planet's volume and causing it to shrink. The process crumpled the surface, creating lobe-shaped scarps or cliffs, some hundreds of miles long and soaring up to a mile high. In the past, the surface was constantly reshaped by volcanic activity , some fairly recently in the planet's past. "The young age of the small scarps means that Mercury joins Earth as a tectonically active planet with new faults likely forming today as Mercury's interior continues to cool and the planet contracts," Tom Watters, Smithsonian senior scientist at the National Air and Space Museum in Washington, D.C., said in a statement .

Mercury is the second densest planet after Earth, with a huge metallic core roughly 2,200 to 2,400 miles (3,600 to 3,800 km) wide, or about 75 percent of the planet's diameter. In comparison, Mercury's outer shell is only 300 to 400 miles (500 to 600 km) thick. The combination of its massive core and abundance of volatile elements has left scientists puzzled for years. A completely unexpected discovery Mariner 10 made was that Mercury possessed a magnetic field. Planets theoretically generate magnetic fields only if they spin quickly and possess a molten core. But Mercury takes 59 days to rotate and is so small — just roughly one-third Earth's size — that its core should have cooled off long ago. "We had figured out how the Earth works, and Mercury is another terrestrial, rocky planet with an iron core, so we thought it would work the same way," Christopher Russell, a professor at the University of California, Los Angeles, said in a statement . An unusual interior could help to explain the differences in Mercury's magnetic field when compared to Earth.

Observations from MESSENGER revealed that the planet's magnetic field is approximately three times stronger at its northern hemisphere than at its southern. Russell co-authored a model that suggests that Mercury's iron core may be turning from liquid to solid at the core's outer boundary rather than the inner. "It's like a snow storm in which the snow formed at the top of the cloud and middle of the cloud and the bottom of the cloud too," said Russell. "Our study of Mercury's magnetic field indicates iron is snowing throughout this fluid that is powering Mercury's magnetic field." The discovery in 2007 by Earth-based radar observations that Mercury's core may still be molten could help explain its magnetism, though the solar wind may play a role in dampening the planet's magnetic field. Although Mercury's magnetic field is just 1 percent the strength of Earth's, it is very active. The magnetic field in the solar wind — the charged particles streaming off the sun — periodically touches upon Mercury's field, creating powerful magnetic tornadoes that channel the fast, hot plasma of the solar wind down to the planet's surface.

Instead of a substantial atmosphere, Mercury possesses an ultra-thin "exosphere" made up of atoms blasted off its surface by solar radiation, the solar wind and micrometeoroid impacts. These quickly escape into space, forming a tail of particles. Mercury's orbital characteristics Mercury speeds around the sun every 88 Earth days, traveling through space at nearly 112,000 mph (180,000 km/h), faster than any other planet. Its oval-shaped orbit is highly elliptical, taking Mercury as close as 29 million miles (47 million km) and as far as 43 million miles (70 million km) from the sun. If one could stand on Mercury when it is nearest to the sun, it would appear more than three times as large as it does when viewed from Earth. Oddly, due to Mercury's highly elliptical orbit and the 59 Earth-days or so it takes to rotate on its axis, when on the scorching surface of the planet, the sun appears to rise briefly, set, and rise again before it travels westward across the sky. At sunset, the sun appears to set, rise again briefly, and then set again.

Mercury is the closest planet to the sun and has a thin atmosphere, no air pressure and an extremely high temperature. Take a look inside the planet. Credit: Karl Tate, SPACE.com Solar System Exploration: Science & Technology: Science Features: Weather, Weather, Everywhere? Weather, Weather, Everywhere? Weather, Weather, Everywhere? Scientists believe that Jupiter's Great Red Spot is actually a hurricane that has been raging for more than 400 years within the planet's atmosphere. Every planet in our solar system has seasons. But the seasons that occur on other planets are extremely different from the traditional spring, summer, fall and winter weather that we experience here on Earth. Despite what may seem like great variations in temperature, weather and climactic conditions in different places around the globe, in reality there actually is little variation in Earth's overall climate. Why? There are several factors that affect the weather on the planets: the tilt of a planet's axis (which causes the seasons), the shape of its orbit around the sun, the presence or absence of a significant atmosphere, its average distance from the Sun, and the length of its day. The tilt of the Earth is the primary reason for the differences in weather we observe between summer and winter.

Earth's axis is tilted about 23 degrees, causing the latitude of the Sun to vary from 23 degrees north of the equator at the beginning of northern summer to 23 degrees south of the equator at the beginning of northern winter. On Earth, that tilt is the primary reason for the differences in weather we observe between summer and winter. Planets with smaller tilts might have smaller weather variations; planets with larger tilts could have more extreme variations. Our orbit is nearly circular, so there is little variation in Earth's overall climate, averaged over both northern and southern hemispheres. But other planets have more elliptical orbits, and therefore their seasonal variations in weather are much different than what we experience. We are much further from the Sun than Mercury or Venus, but closer than the other six planets. Generally, weather variations are more pronounced for those planets closer to the Sun. The terms "summer" and "winter" tend to be Earth-oriented terms but can be applied to the other planets as well. When the North Pole of any planet is tilted toward the sun, astronomers call it the Summer Solstice; when the South Pole is tilted toward the sun it's called the Winter Solstice.

So, how do seasons and weather conditions stack up on other planets? Mercury experiences some of the most bizarre conditions. Until the 1960's, it was thought that Mercury's day was the same length as its year, keeping the same face to the Sun, much as the Moon does to Earth. But we now know that Mercury rotates three times during two of its years. With this bizarre 2:3 ratio, Mercury is the only body in the solar system locked into an orbit-to-rotation ratio other than 1:1. This fact and the high eccentricity of Mercury's orbit cause very strange effects if an observer were to stand on Mercury's surface. At some longitudes the observer would see the Sun rise and then gradually increase in apparent size as it slowly moves toward the zenith. At that point the Sun would stop, briefly reverse course, and stop again before resuming its path toward the horizon, and decrease in apparent size. It is the motion of the Sun against the background stars, which varies for an observer on Mercury. Observers at other points on Mercury's surface would see different but equally bizarre motions. That makes it impossible to really tell when one season ends and the next one begins.

And, to add to the uniqueness of the planet, temperature variations on Mercury are the most extreme in the solar system, ranging from -280?F at night to 800 degrees F during the day for parts of the surface. And yet near Mercury's poles there is almost no change in temperature, because, in spite of its very long duration between sunrises (176 Earth days), the tilt of its axis is zero, meaning that there are no seasonal variations on Mercury. Furthermore, with essentially no atmosphere, Mercury's weather changes are displayed not as storms in the atmosphere, but as wide swings in surface temperature. Venus has a very small axial tilt -- 3 degrees versus Earth's 23.5 degrees. Its dense, acidic atmosphere produces a runaway greenhouse effect that keeps the surface at around 865 degrees F year-round, which is hot enough to melt lead. Venus also has a smaller orbit than Earth, which makes its seasons shorter, and variations in temperature and conditions extremely slight. Its seasons last a mere 55-58 days, as opposed to 90-93 days on Earth.

In fact, circumstances combine to make Venus' seasons shorter than its days: successive sunrises on Venus are separated by 117 Earth days, and Venus rotates backwards, causing the Sun to rise in the west and set in the east. When the Magellan spacecraft made its historic dramatic final fiery descent into Venus' atmosphere on October 11, 1994, it was northern springtime on Venus, while in the peak of northern autumn here on Earth. Mars' winds were strong enough to give the rover Spirit a good cleaning. Mars has one of the highest orbital eccentricities of any planet in our solar system (other than Mercury and Pluto) -- its distance from the Sun varies between 1.38 and 1.67 AU over the Martian year. This large variation, combined with an axial tilt slightly greater than Earth's, gives rise to seasonal changes far greater than we experience here on Earth. On Mars, dramatic dust storms are common due to solar heat, which warms the Martian atmosphere and causes its air to move rapidly, lifting dust off the ground.

Because the Martian atmosphere is thin -- about 1% as dense as Earth's at sea level -- only the smallest dust grains hang in the air, and the grains are as fine as smoke. One of the strangest effects of seasons on Mars is the change in atmospheric pressure. During winter the global atmospheric pressure on Mars is 25% lower than during summer. This happens because of the eccentricity of Mars's orbit and a complex exchange of carbon dioxide between the Martian dry-ice polar caps and its CO2 atmosphere. Around the winter solstice when the North Pole is tilted away from the sun, the northern polar cap expands as carbon dioxide in the polar atmosphere freezes. At the other end of the planet the southern polar cap melts, giving CO2 back to the atmosphere. This process reverses half a year later at the summer solstice. But Mars is 10% closer to the Sun in southern summer than it is in northern summer. At the time of the winter solstice the northern polar cap absorbs less CO2 than the southern polar cap absorbs half a year later. The difference is so great that Mars's atmosphere is noticeably thicker during northern winter.

Its orbital motion is slowest when it is at aphelion (the farthest point from the Sun) and fastest at perihelion (the closest point to the Sun). This makes Martian seasons vary greatly in duration than those on Earth. Seasons change roughly every six months, with northern spring and fall lasting 171 Earth days, northern summer being 199 days in length, and northern winter being only 146 days. Because of these variations, Martian seasons do not start at the same Earth day each Martian year. Jupiter , like Venus, has an axial tilt of only 3 degrees, so there is literally no difference between the seasons. However, because of its distance from the sun, seasons change more slowly. The length of each season is roughly three years. Jupiter is the fastest spinning planet in our Solar System, which causes the planet to flatten at the poles and bulge at the equator. Also, like Saturn, Uranus, and Neptune, Jupiter has a very dense, turbulent atmosphere that can cause dramatic storm activity. For example, the Hubble Space Telescope took a detailed look at a unique cluster of three immense oval-shaped storms that occurred below Jupiter's Great Red Spot, in 1995.

Scientists believe that Jupiter's Great Red spot is actually a hurricane that has been raging for more than 400 years within the planet's atmosphere. The temperature on Jupiter also varies widely, because of the different chemical compositions that make up its atmosphere. For example, the highest white clouds are made of crystals of frozen ammonia, and the temperature here is about -220 F (-140 degrees C). Measurements made by ground instruments and spacecraft show that Jupiter's temperature increases with depth below the clouds, and the temperature reaches 70 degrees F (21 degrees C) -- "room temperature" -- at a level where the atmospheric pressure is about 10 times as great as it is on Earth. As you travel further into the interior of Jupiter, the temperature becomes even hotter -- at the planet's core, it is even hotter than the Sun! Cassini captures Saturn's stormy surface. Saturn has an axial tilt of almost 27 degrees, which is slightly larger than that of Mars. But when talking about a gas giant in the outer reaches of the solar system, the concept of seasonal change doesn't quite mean the same as on Earth. Seasonal variations are strong on Saturn and each season lasts more than 7 years.

That's a long winter! When the Cassini spacecraft began its revolutionary mission to Saturn and its largest moon, Titan, Saturn was two years into its northern fall season. When it arrived at Saturn in 2004, it will have just become northern winter on the ringed planet. Uranus has a relatively circular orbit, so it remains at about the same distance from the Sun throughout its long year. But the axis of Uranus is tilted by 98 degrees! This causes 21-year-long seasons and unusual weather, although one thing that is certain: it is always cold. For nearly a quarter of the Uranian year (equal to 84 Earth years), the sun shines directly over each pole, leaving the other half of the planet plunged into a long, dark winter. Uranus has a deep atmosphere of mostly hydrogen and helium. Absorption of red light by methane in the atmosphere gives the planet its bluish color. Early visual observers reported Jupiter-like cloud belts on the planet, but when the Voyager 2 spacecraft flew by in 1986, Uranus appeared virtually featureless. The Northern Hemisphere of Uranus is just now coming out of the grip of its decades-long winter.

As the sunlight reaches some latitudes for the first time in years, it warms the atmosphere and triggers gigantic springtime storms comparable in size to North America with temperatures of 300? F below zero. By the year 2007, the sun will be shining directly over Uranus' equator, which will produce more evenly distributed sunlight and the ability to see features at all latitudes on Uranus. Neptune has an axial tilt of 28.5 degrees, which isn't too much different than Earth's. But this gas giant doesn't really experience appreciable seasonal variation, although its seasons last for more than 40 years! Because Pluto is so far away, virtually nothing is known about its seasons. However, because of its tilt of nearly 120 degrees and the highest eccentricity of any planetary orbit even at its great distance from the Sun, weather variations are expected to be significant -- perhaps enough to result in far greater changes in its atmospheric pressures than even that of Mars. It is possible that the very thin atmosphere of Pluto may entirely freeze and fall as snow to Pluto's surface as it gets farther and farther from the Sun. Extraterrestrial weather and seasons are harsh and may be rather unpredictable.

So, as we contemplate the different times of year on Earth, and may lament about the coming of a long, hot summer or a cold harsh winter, take a quick mental tour of our solar system. Suddenly, having to water the garden or scrape ice off of a windshield doesn't seem so bad. Last Updated: 21 January 2014 The Solar System Explained | HowStuffWorks The Solar System Explained NEXT PAGENEXT Astronomers sometimes use light that can't be seen by humans to learn more about objects in space. This picture of the sun was taken using only ultraviolet light. As you can tell, it looks different from a picture using visible light. See more space exploration pictures . Photo courtesy of NASA Our planet Earth is part of a solar system that consists of nine (and possibly ten) planets orbiting a giant, fiery star we call the sun. For thousands of years, astronomers studying the solar system have noticed that these planets march across the sky in a predictable way. They've also noticed that some move faster than others . . . and some seem to be moving backward. What's an accretion disk?

The Sun: The Center of Our Solar System The sun (which, incidentally, is only a medium-size star) is larger than any of the planets in our solar system. Its diameter is 1,392,000 kilometers (864,949 miles). Earth's diameter is only 12,756 kilometers (7,926 miles). More than one million Earths could fit inside the sun. The large mass of the sun produces an enormous gravitational pull that keeps all the planets of the solar system in their orbits. Even Pluto, which is six billion kilometers (3,728,227,153 miles) away, is kept in orbit by the sun. Planets in Our Solar System Each planet in our solar system is unique, but they all have a few things in common, too. For example, every planet has a north and a south pole. These points are in the center of the planet at its ends. A planet's axis is an imaginary line that runs through the center of the planet and connects the north and south poles. The imaginary line that runs around the planet at its middle (like your waist) is called its equator.

While every planet rotates on its axis, some planets rotate quickly and some rotate slowly. The time that it takes for a planet to rotate once on its axis is its rotation period. For most planets in our solar system, the rotation period is close to the length of its day. (A day length is the time between sunrises at the same point on the planet.) Mercury and Venus are exceptions. As each planet in our solar system rotates on its axis, it also revolves around the sun. The time that it takes for a planet to make a complete revolution around the sun is the planet's year. The path that the planet follows around the sun is called its orbit. Different planets have different orbits — and orbits can take different shapes. Some orbits are nearly circular and some are more elliptical (egg-shaped). What Else Is in Our Solar System? Although we tend to think only about the sun and the planets when we consider our solar system, there are many other types of bodies that huddle around the sun along with Earth and its planetary brothers and sisters. The solar system includes moons (and some of those moons have moons), supernova explosions, comets, meteors, asteroids, and plain old space dust.

To be sure, there are more objects in our solar system, some of which have yet to be discovered. What's This About a Tenth Planet in Our Solar System? A name like 2003 UB313 doesn't sound very exciting, but this far-flung body of rock and ice has rocked the world of astronomy. At about 3,000 kilometers (1,864 miles) across, it is a bit larger than Pluto, and it looks to be a lot farther away — about three times as far. But it does travel in the same circles (orbitpaths) as the other nine planets in the solar system. There isn't a question about its presence. It has been sighted from quite a few spots (the Palomar Observatory and the Gemini North telescope on MaunaKea to name two). The real question is: What constitutes a planet? And does 2003 UB313 meet the criteria? It has been 75 years since the last planet was discovered in our solar system and the International Astronomical Union is still debating whether Pluto qualifies as a planet.

On the other hand, NASA has referred to 2003 UB313 as our tenth planet, a pretty hefty endorsement by any standard. Maybe 75 years from now they'll still be debating over its status. Oh, Those Retrograde Planets If you spend time observing the solar system, you will notice that some planets — especially Venus and Mercury — seem to move backward in the sky. These planets don't really move backward, but they appear to move backward because their position in relation to Earth is changing. It's the same thing that happens when your car passes another car on the highway. The car you are passing seems to be going backward, but it's only because your car has gone past it. This odd backward motion is called "retrograde motion." A planet can also have "retrograde rotation," which means it rotates in the opposite direction of its orbit. Most planets in our solar system have "prograde rotation," which means they rotate in the same direction as their orbits. Why is Earth rotating? Did it always have the same rotation period? Will it always have the same rotation period? Audio recording of Dr. Marc reading this page. Click play to hear me read this to you!

Earth's graceful 24-hour rotation rate is one of the traits that makes our planet so friendly to life, allowing most parts of Earth to stay a nice, comfortable temperature as they are bathed in sunlight during the day and darkness at night. Each planet in the solar system has its own unique rotation rate. Tiny Mercury, sizzling closest to the Sun, takes 59 Earth days to turn around just once. Venus, the second planet, rotates once every 243 Earth days. What's more, Venus rotates backwards from the direction of its orbit around the Sun, as do Uranus and tiny dwarf planet Pluto. Uranus even lies down on the job, rolling around with its axis of rotation pointed nearly toward the Sun. Why do Earth and the other planets rotate at all? It will help to understand how our solar system formed. Almost five billion years ago, our solar system had its beginnings as a vast cloud of dust and gas. The cloud began to collapse, flattening into a giant disk that rotated faster and faster, just as an ice skater spins faster as she brings her arms in.

The Sun formed at the center, and the swirling gas and dust in the rest of the spinning disk clumped together to produce the planets, moons, asteroids, and comets. The reason so many objects orbit the Sun in nearly the same plane (called the ecliptic) and in the same direction is that they all formed from this same disk. While the planets were forming, there was not much peace in our solar system. Clumps of matter of all sizes often collided, and either stuck together or side-swiped each other, knocking off pieces and sending each other spinning. Sometimes the gravity of big objects would capture smaller ones in orbit. This could be one way the planets acquired their moons. Scientists think that a large object, perhaps the size of Mars, impacted our young planet, knocking out a chunk of material that eventually became our Moon. This collision set Earth spinning at a faster rate. Scientists estimate that a day in the life of early Earth was only about 6 hours long. The Moon formed much closer to Earth than it is today. As Earth rotates, the Moon's gravity causes the oceans to seem to rise and fall.

(The Sun also does this, but not as much.) There is a little bit of friction between the tides and the turning Earth, causing the rotation to slow down just a little. As Earth slows, it lets the Moon creep away. We can use extremely accurate atomic clocks to measure exactly how much the rotation is slowing down. One hundred years from now, a day will be about 2 milliseconds longer than today. Two milliseconds is 1/500th of a second, or how long it takes a car going 55 mph to travel only 2 inches--in other words, much less than the blink of an eye. So, if you live to be 100, you can't complain that the days are getting shorter! At this rate, though, you don't have to worry about the days getting enough longer to change things very much. Learn more about the great variety of planets and moons in the solar system by playing Solar System Switch-a-roo . Why and how do planets rotate? - Scientific American Scientific American Report Ad George Spagna, chair of the physics department at Randolph-Macon College, explains. Stars and planets form in the collapse of huge clouds of interstellar gas and dust.

The material in these clouds is in constant motion, and the clouds themselves are in motion, orbiting in the aggregate gravity of the galaxy. As a result of this movement, the cloud will most likely have some slight rotation as seen from a point near its center. This rotation can be described as angular momentum, a conserved measure of its motion that cannot change. Conservation of angular momentum explains why an ice skater spins more rapidly as she pulls her arms in. As her arms come closer to her axis of rotation, her speed increases and her angular momentum remains the same. Similarly, her rotation slows when she extends her arms at the conclusion of the spin. As an interstellar cloud collapses, it fragments into smaller pieces, each collapsing independently and each carrying part of the original angular momentum. The rotating clouds flatten into protostellar disks, out of which individual stars and their planets form. By a mechanism not fully understood, but believed to be associated with the strong magnetic fields associated with a young star, most of the angular momentum is transferred into the remnant accretion disk. Planets form from material in this disk, through accretion of smaller particles.

In our solar system, the giant gas planets (Jupiter, Saturn, Uranus, and Neptune) spin more rapidly on their axes than the inner planets do and possess most of the system's angular momentum. The sun itself rotates slowly, only once a month. The planets all revolve around the sun in the same direction and in virtually the same plane. In addition, they all rotate in the same general direction, with the exceptions of Venus and Uranus. These differences are believed to stem from collisions that occurred late in the planets' formation. (A similar collision is believed to have led to the formation of our moon.)

Question: Which planet in our soar system spins on its axis faster than any of the other planets?
Answer: JUPITER